1. Field of the Invention
The present invention generally relates to bone stabilization systems, and more particularly to a transverse connector for connecting adjacent rods of orthopedic stabilization systems. The transverse connector, or cross-link, may connect together adjacent spinal rods of a spinal stabilization system.
2. Description of Related Art
Bone disorders, degenerative conditions, or trauma may result in a need to stabilize a bone or bones of a patient with an orthopedic stabilization system. For example, disease or trauma may result in the need to stabilize the spine of a patient. A variety of systems may be used to stabilize a spine. A spinal stabilization system may generally be classified as an anterior, lateral, or posterior system according to a position of the system relative to the spine. Posterior stabilization systems often include pairs of vertically aligned rods for stabilizing both short and long segments of a spine.
An orthopedic stabilization system may include a pair of rods that are coupled to a bone or bones. For example, a posterior spinal stabilization system may include a pair of bendable rods that are contoured and longitudinally disposed adjacent to vertebral bodies of a spine. A pair of rods of an orthopedic stabilization system may be coupled to a bone or bones by fixation elements. The fixation elements may include, but are not limited to, hooks and bone screw connectors.
Rods of an orthopedic stabilization system may be oriented so that the rods are substantially parallel to each other. Alternately, rods of an orthopedic stabilization system may be oriented so that the rods are skewed relative to each other. In a skewed orientation, the rods may be oriented towards each other so that a horizontal distance between the rods is not constant. In other words, the rods may not be horizontally parallel to each other. FIG. 1 shows a top view of a pair of rods 28 that are not horizontally parallel. Also, the rods 28 may be oriented so that a vertical distance between the rods is not constant. In other words, the rods 28 may not be vertically parallel to each other. FIG. 2 shows a pair of rods that are not vertically parallel.
Transverse connectors may be attached to connect adjacent rods of an orthopedic stabilization system together. Transverse connectors may provide rigidity to a stabilization system. Transverse connectors may also inhibit rod movement. Stresses may act to return a stabilized bone system to a deformed position. For example, stresses on a spine and on a spinal stabilization system often operate to return a corrected spine to a deformed position. Transverse connectors may inhibit rod movement of the spinal stabilization system during a post-operative period so that the spine remains in a corrected position.
Many transverse connectors have been developed that link adjacent rods together. U.S. patents and patent application Ser. No. 09/093,756 to Wagner et al.; U.S. Pat. No. 5,980,521 to Montague et al.; U.S. Pat. No. 5,947,966 to Drewry et al.; U.S. Pat. No. 5,752,955 to Errico et al.; U.S. Pat. No. 5,709,684 to Errico et al.; and U.S. Pat. No. 5,667,507 to Errico et al., describe transverse connectors. Each of these patents and patent applications are incorporated by reference as if fully set forth herein. Many transverse connectors present one or more problems for a surgical team that installs the transverse connectors. Some of the problems associated with transverse connectors include the need to pre-load connectors on a rod, high profiles, wide profiles, separate component fasteners, and proper tightening of threaded fasteners. Also, the ability of a transverse connector to connect rods that are skewed relative to each other may be problematic.
Some transverse connectors have engaging members that must be preloaded onto a rod prior to the rod being placed within a patient. The use of preloaded connectors may require significant pre-operative planning. The use of preloaded connectors may inhibit a surgical team's ability to make changes that are needed to meet conditions presented during insertion of the stabilization system in the patient. Other transverse connectors include rod openings that allow the transverse connector to be placed on rods after the rods have been attached by fixation elements to a patient.
Some transverse connectors may have a high profile and/or a wide profile. These profiles may cause surgical complications to tissue and bone adjacent to the connector. A rod fastening system that attaches the transverse connector to the adjacent rods may cause a high or wide profile. For example, a connector that snaps onto a spinal rod may be attached to a transverse connector by a nut that engages a threaded shaft of the connector. The nut and shaft may cause the assembled transverse connector to have a high profile and a wide profile. A high profile transverse connector may result in abrasion of tissue adjacent to the transverse connector. A wide profile transverse connector may require the removal of a portion of bone to allow the transverse connector to be attached to stabilization rods. A slim profile may require less or no bone removal when the transverse connector is attached to stabilization rods.
Some transverse connector rod fastening systems may require separate component fastening members to securely attach the transverse connector to stabilization rods. A separate component fastener, such as a nut, may be difficult to properly position and secure during an installation procedure.
A transverse connector must be securely tightened to a stabilization rod. Some rod fastening systems of transverse connectors use threaded fasteners to attach the transverse connector to adjacent rods. The threaded fastener typically is a setscrew or a nut. Not tightening a threaded fastener enough may allow movement of the transverse connector. Over tightening a threaded fastener may result in damage to the fastening system that could cause failure of the transverse connector. Applying a proper amount of torque to a threaded fastener may require the use of a torque wrench. Using a torque wrench may be burdensome to a surgical team that installs a stabilization system. Also, a torque wrench may require frequent calibration to ensure that an indicated amount of torque is applied when the torque wrench is used.
A threaded fastener such as a setscrew may need to be angled within the body so that a contact portion engages a rod sufficiently to secure the rod to the transverse connector. One type of transverse connector that utilizes a setscrew operates by contacting the setscrew against a lower portion of a rod to drive a top portion of the rod against a body of the transverse connector. The angle of the setscrew may be less than about 45° with respect to a longitudinal axis of the transverse connector. The angle of the setscrew may require an insertion tool with a flexible shaft to fix the rod to the transverse connector. Alternately, a large opening may be made in the patient so that an insertion tool without a flexible shaft may be used to fix the rod to the transverse connector. Another type of transverse connector that utilizes a setscrew operates by contacting the setscrew against an upper portion of a rod to drive a lower portion of the rod against a body of the transverse connector. Positioning a pair of rods within such a transverse connector may be difficult during installation of the transverse connector in a patient.
A transverse connector may include a body, a pair of rod openings in the body, and rod engagers. The body of the transverse connector may span a distance between a pair of rods. The body may have a fixed length, or the length of the body may be adjustable. Bending the body may adjust the length of the body and the orientation of the rod openings relative to the rods. Alternately, the length of the body may be adjustable by adjusting a position of a first section of the body relative to a second section of the body. After the positions of the first section and the second section are adjusted, the first section and the second section may be fixed using a fastener. The fastener may be, but is not limited to, a setscrew or a nut and bolt. The pair of rod openings may hold rods of a bone stabilization system. The rod engagers may be used to attach rods that are positioned in the rod openings to the body of the transverse connector.
A pair of rods of a stabilization system may be skewed relative to each other in both a vertical plane and a horizontal plane. Some transverse connectors cannot be adjusted to accommodate rods that are horizontally and/or vertically skewed. Other transverse connectors require a portion of the transverse connector to be bent to accommodate the skew of the rods.
A distance between a pair of rods of an orthopedic stabilization system may determine positions of rod fastening systems within a transverse connector. For transverse connectors that are attached to a pair of closely spaced rods, the rod fastening systems may be located on outer sides of the rod openings. For transverse connectors that are attached to a pair of rods that are spaced a farther distance apart, one rod fastening system may be located on an outer side of a rod opening and the other rod fastening system may be located between the two rod openings. Alternately, both rod fastening systems may be located between the rod openings. Also, for transverse connectors that are attached to a pair of rods that are spaced a large distance apart, an adjustable length transverse connector may be used.